Duplicate Digit Determination IV (Posted on 2011-06-05)

(I) Each of x and y is a positive integer with x < y such that, reading from left to right, the first two digits in the base ten expansions of 1978^{x} and 1978^{y} are congruent.

Determine the minimum value of x+y.

(II) What is the minimum value of x+y - if, keeping all the other conditions in (i) unaltered, the first three digits in the base ten expansions of 1978^{x} and 1978^{y} are congruent?

Note: None of the expansions of 1978^{x} and 1978^{y} can contain any leading zero.